A backhoe apparatus is a particularly versatile piece of equipment which can be used for a wide variety of operations. A conventional backhoe apparatus includes an elongated boom member and dipper arm assembly mounted to a rear of a material handling implement such as a tractor or the like thereby providing mobility for the backhoe apparatus in use while further facilitating transportation of the backhoe apparatus from one location to another.
Bending and torsional loads of great magnitude can be and often are exerted on the boom member and dipper stick assembly during operation of the backhoe apparatus. Thus, it is necessary that the boom member and dipper stick assembly be designed with heavy construction strong enough to withstand substantial loading placed thereon during normal operations of the backhoe apparatus.
The heavy construction of the boom member and dipper stick assembly result in a backhoe apparatus having substantial weight. In that the backhoe apparatus is typically attached to a rear end of the implement, at a position rearward of the rear wheels thereof, there is a natural tendency for the rear wheels of the implement to serve as a fulcrum point about which the weight of the backhoe apparatus tends to rock the implement backwards. Even when the backhoe apparatus is positioned for transport, the main center of gravity for the implement is far to the rear such that implement stability is effected and handling is unduly difficult.
On conventional backhoes, mechanical balance is attempted by placing counterweights on the front of the implement. As will be appreciated, counterweights have the disadvantage of increasing the total weight of the implement and are usually insufficient to overcome inertial movements caused by the shifting weight of the backhoe apparatus as the implement is driven from one location to another.
The elongated boom member of a typical backhoe apparatus has one end mounted to a rear end of the implement for vertical and sideways movements relative thereto. The elongated dipper stick arm is connected toward an opposite end of the boom member. A dipper, or other suitable tool, is typically mounted to the distal end of the dipper stick arm to effect digging or other work operations.
The benefits of moving the backhoe apparatus into a transport position whereat the boom member is raised to a generally vertical orientation and the dipper is folded in as close as possible to the boom were recognized early on by J. I. Case Company. Although this concept advantageously brought the center of gravity of the backhoe apparatus closer to the implement, the main center of gravity of the implement, relative to the rear wheels, continued to be a problem and implement handling remained somewhat unstable.
In responding to these problems, J. I. Case Company has for many years provided a backhoe apparatus having an advantageous overcenter design. Such a backhoe apparatus includes a generally U-shaped swing tower having a linear boom member pivotally connected about a lower pivot axis on the swing tower. The swing tower is connected to the implement for lateral swinging movement allowing the boom member, dipper arm, and dipper to move sideways relative to the implement. In early J. I. Case designs, a pair of outboard boom cylinders attach to and flank the boom member and connect to an upper pivot axis on the swing tower. The swing tower is configured such that when the backhoe apparatus is moved from a transport position to an operating position, the linear boom member is vertically moved from one side of the upper pivot axis to an opposite side of the pivot axis. In the transport position, the boom member is allowed to swing somewhat downwardly and toward the implement. The ability of the boom member to assume a more forwardly inclined relationship enhances the position of the main center of gravity for the implement thereby providing better balance and handling characteristics therefor.
Arranging the boom cylinders on opposite lateral sides of the boom member, however, has certain operational drawbacks. With the boom cylinders arranged in flanking relationship relative to the boom member, they are exposed for possible damage when the backhoe apparatus is laterally moved sideways relative to the implement. Moreover, with the boom cylinders arranged in flanking relationship relative to the boom member, they can limit the working depth obtainable by the backhoe apparatus by adversely interfering with the vertical reach or movement of the boom member beneath surface levels. As will be appreciated visibility is also adversely affected by disposing the cylinders in flanking relationship relative to the boom member in that the effective width of the boom is widened thereby hindering visibility directly rearward of the boom.
The advantages of being able to move the boom member of a backhoe apparatus overcenter were recognized in the industry and likewise embodied in later J. I. Case Company designs. In more recent J. I. Case Company backhoe apparatus designs, the boom member consists of two laterally spaced apart boom sections. The laterally spaced apart boom sections make it possible to use a single boom cylinder which is mounted between the boom sections. As in earlier designs, overcenter forward movement of the boom provides a stable transport configuration for the backhoe apparatus.
Providing two outboard boom sections in flanking relationship to the boom cylinder, however, substantially enlarges the width of the boom. The enlarged boom width requires a larger swing tower for pivotally securing the boom to the implement. The increase in boom width furthermore hinders visibility to work areas directly behind the boom through the opening provided between the boom sections. Moreover, due to the position of the cylinder and reduced size and shape of the two boom sections, the effective cross-sectional configuration of the boom is limited in torsional rigidity. Limiting torsional rigidity of the boom, of course, likewise limits effectiveness and capacity of the backhoe apparatus to handle the substantial loading placed on the backhoe apparatus during normal operations.
Thus, there is a need and a desire for an overcenter backhoe apparatus which protects the boom cylinder from damage without limiting working depth while providing torsional rigidity for the boom to enhance performance characteristics of the backhoe apparatus.